HYSTERESIS MOTOR:
These motors consist of a chrome-steel cylinder of high retentivity so that the hysteresis loss is high. It has no winding. Once the magnetic polarities are induced in the rotor, it revolves synchronously with the revolving magnetic field. Since the rotor has no slots or winding, the motor is noiseless free from vibrations. Such a motor is ideal for sound equipment.
SUMMARY OF CHARACTERISTICS AND APPLICATIONS OF SINGLE PHASE MOTOR:
| Motor type | Main characteristics | Applications |
Poor starting torque. Non-reversing drives with
Low power factor and efficiency. light loads on starting.
Shunt speed characteristics.
Capacitor motor:
Moderately good starting torque. Suitable for reversing as well as
Higher power factor and efficiency non reversing drives without heavy starting
than split phase type. Quiet operation loads Used in passenger lifts, domestic shunt speed characteristics. refrigerators, fans, etc.
Repulsion:
Good starting torque. Shunt speed Suitable for heavy starting
characteristics. .
Additional winding needed for reversing.
Universal (Series):
Good starting torque. High power factor. Vacuum cleaners, motorized hand tools.
Small Synchronous motor:
Constant speed operation. clocks, timing mechanisms,
Poor starting picture and sound reproduction.
Low power factor.
Mathematical analysis of single phase motor:
According to rotating field theory:
They are 2 rotating fields, Ff forward rotating field and Fb - Backward rotating field. Slip of rotor w.r.t forward rotating field is
Ns = (120 F) / P R.P.M.
Slip of rotor w.r.t backward rotating field :
2-s ωs= (2 π Ns)/60 rad/sec.
Rotating field Equivalent Single φ motor under running condition
Vf and Vb are components of stator voltage Vm.
Main winding current.
Im = Vm/ |Ztotal| = Vm/ |Zf/2 + Zb/ 2|
At x =m, magnetizing current is neglected.
The Circuit Model of Single-phase, single-winding motor is shown in the figure below :
Air gap power for forward field, pgf = ½ I 2m Rf
Air gap power for backward, pgb = ½ I 2m Rb
Rf and Rb are real parts of Zf’ and Zb’
Torques produced by 2nd fields
Tf = 1/ωs Pgf and Tb = 1/ωs Pgb
ωs = synch. Speed in rad/sec
Total torque. T= Tf – Tb = 1/ ωs (Pgb - Pgb) = I2m/2 ωs (Rf - Rb)
Total rotor Cu loss: Rotor Cu loss corresponding to forward field + rotor Cu loss corresponding to backward field
S. Pgb + (2-s) Pgb
Total electric power. connected to gross mech-form
Pm = (1-s) ωs T = (1-s) (Pgf - Pgb) = (1-s) Pgf + [1-(2-s)]Pgb
Total electric power input to motor.
P Elect = Pgf + Pgb
Simplified formula
Emf/Emb = (r2/s + jX2 )/ (r2/2-s + jX2) at X = infinity
Impedence offered to Vf component, Zf= ½ [{r1m + r2/(2-s}}]+ j (X1 + X2)
Impedence offered to Vb component, Zb= ½ [{r1m + r2/(2-s}}]+ j (X1 + X2)
Z total = Zf + Zb Vf/Vb= Zf/Zb
Tf/Tb= Pgb/Pgb = (2-s)/s, Tf=1/ I2m r2/2s
Tb=1/ ωs I2 m r2/(2(2-s))
Ttotal = Tf - Tb = (I2mr2)/2 ωs [1/s – 1/ (2-s)]Nω-m
Tf/Ttotal = [1/s]/[1/s – 1/(2-s]],
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